Power cable splice

ABSTRACT

The power cable splice includes two cables, the stripped respective end portions of which are interconnected by a metal connector and are covered by a splice body and by electrical shielding. The splice further includes a flexible composite plate including a first layer that is semiconductive, and a second layer that is not electrically conductive, the plate being wrapped around the connector and around the ends of the stripped insulation of the cables, with the semiconductive layer of the plate being in contact with the connector.

The present invention relates to a power cable splice.

BACKGROUND OF THE INVENTION

A medium-voltage or high-voltage electrical power cable includes aconductor, insulation on the conductor, a semiconductive screen, a metalscreen, and an outer sheath.

In order to splice together two such power cables, an end portion ofeach of them is prepared so as to strip the semiconductive screen, theinsulation, and the conductor in successive steps and over suitablelengths, with the metal screen itself optionally being stripped. Thestripped conductors are then electrically and mechanically connectedtogether by means of a connector. Over the end portions of the cables,the removed screens and the usually removed outer sheath arereconstituted by means of firstly a splice body surrounding theconnector and extending on either side thereof, secondly electricalshielding on the splice body, and optionally thirdly an outer protectionthat covers the electrical shielding and that extends over the end ofthe outer sheath of each cable.

Splices implemented in this way are disclosed in particular in DocumentsFR-A-2 436 519 and U.S. Pat. No. 4,742,184. In such a known splice, thesplice body is a tubular element comprising at least two layers formedby an insulating main layer and a semiconductive outer layer.

In the splice disclosed in Document FR-A-2 436 519, the splice body isshrink-fittable, and in particular heat-shrinkable. It may include avoltage-gradient inner layer which is semiconductive or has non-linearelectrical resistivity characteristics, or which includes a fluidcoating such as a mastic. Furthermore, before the splice body isinstalled, the space adjacent to the stripped and interconnectedconductors may be provided with a filler material which may be asilicone grease, a mastic, or a meltable glue, and may have insulating,conductive, or semiconductive properties, for filling any voids thatremain under the splice body as installed, so as to minimize the risksof insulation breakdown due to the air in certain voids ionizing.

In the splice disclosed in Document U.S. Pat. No. 4,742,184, the splicebody includes a semiconductive inner layer, and the electricallyinterconnected cables are provided firstly with a split semiconductiveelastomer tube mounted on the connector, and secondly with an insulatingelastomer tube mounted on the stripped insulation of each of the cables.The tubes adapt the outside diameter of the cables to fit the insidediameter of the splice body. Accordingly, they are chosen as a functionof the cables used and/or of the connector used, so as to couple thelayers of the splice body to the corresponding layers of the cables. Thesemiconductive elastomer tube also co-operates with the semiconductiveinner layer of the splice body to place outside the influence of theelectric field any air gaps between the splice body and the stripped andinterconnected conductors. The semiconductive inner layer extends forthis purpose along the semiconductive elastomer tube and over the facingend of each of the two insulating tubes.

Installing those known means for minimizing the risk of insulationbreakdown in power cable splices is time-consuming and/or difficult orsometimes even dangerous when a flame is used for shrinking theheat-shrinkable splice body, and, once installed, they may be moved, orremoved in part during installation of the splice body when said splicebody is mechanically shrink-fittable.

SUMMARY OF THE INVENTION

An object of the invention is to provide means that avoid thoseproblems, that are very easy and quick to install, that are adapted toany type of connector and to any type of cable, and that significantlyimprove the breakdown strength of the splice.

The invention provides a power cable splice including:

two cables, each of which comprises a conductor, insulation, asemiconductive screen, a metal screen, and an outer sheath, and has anend portion that has been stripped in successive steps;

a metal connector interconnecting the stripped conductors;

means that are electrically conductive at least in part and thatsurround said connector;

a tubular splice body surrounding said means and extending over the endsof the stripped insulation of the cables; and

electrical shielding surrounding the splice body and electricallyconnected to the metal screens of the cables;

said splice being characterized in that said means are constituted by aflexible two-layer composite plate which comprises a first layer of atleast semiconductive material, and a second layer of a material that isnot electrically conductive, and which has a length not less than thelength of the stripped and interconnected conductors, and a width notless than the peripheral length of said connector, said plate being laidalong and wrapped around said connector with said first layer being incontact with the connector.

The splice advantageously has at least one of the following additionalcharacteristics:

said composite plate is made up of a semiconductive elastomer platedefining said first layer, and of a mastic plate defining said secondlayer, the two plates being mutually superposed and secured to eachother;

said composite plate is extruded;

the length of said composite plate is significantly longer than that ofthe stripped and interconnected conductors, and said plate is wrappedover the ends of the stripped insulation of the cables;

the first layer has at least one of its dimensions smaller than thecorresponding dimension of said second layer;

the splice further includes a strip made of an adhesive material andassociated with said composite plate for fixing it along said connector;

said splice body includes an insulating main layer, a semiconductiveouter layer, and optionally a voltage-gradient continuous inner layermade of a material having high permittivity; and

said splice body is a mechanically shrink-fittable element.

BRIEF DESCRIPTION OF THE DRAWING

The characteristics and advantages of the present invention appear fromthe following description of a preferred embodiment given by way ofexample and with reference to the accompanying drawing, in which:

FIG. 1 is a view partially in section and partially in elevation of asplice according to the invention whereby two power cables are splicedtogether;

FIG. 2 is a view of a composite plate of the splice, the plate beingshown in the deployed state before it is installed; and

FIG. 3 shows a strip of adhesive material, advantageously also used inthe splice of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, the power cable splice includes two medium-voltageor high-voltage cables 1 and 2, whose respective end portions arestripped, connected together, and equipped so that they are functionallyreconstituted.

As shown and referenced on cable 1 only, each cable comprises a centralconductor 3, insulation 4 surrounding the conductor, optionally with asemiconductive layer being disposed therebetween, a semiconductivescreen 5 on the insulation, a metal screen 6 on the semiconductivescreen, and a protective outer sheath 7. The cable end portions to beconnected together are stripped in successive steps by successivelyremoving suitable lengths of the outer sheath, of the screens, and ofthe insulation, with the metal screen optionally not being strippedrelative to the outer sheath.

A metal connector 9 of any suitable type electrically and mechanicallyinterconnects the two stripped conductors of the cables.

The splice including the two cables interconnected in this way alsoincludes a flexible composite plate 10 which surrounds the connector 9and extends along the connector and over the end of the strippedinsulation of each cable, a splice body 11 which surrounds the compositeplate as installed and extends over the end of the semiconductive screenof each cable, electrical shielding 12 which covers the splice body andis electrically connected to the metal screens of the cables, and,preferably and as shown, outer protection 13 which then covers theshielding and extends over the ends of the sheaths of the cables.

The composite plate 10 comprises two layers, namely a layer of materialthat is semiconductive or conductive 10A, and a layer of material thatis not electrically conductive 10B, the layers being mutually superposedand secured to each other. Layer 10A is preferably made of asemiconductive elastomer material and formed by a plate made of suchmaterial. Layer 10B is advantageously formed by a plate made of mastic,preferably having high permittivity, i.e. approximately equal to orgreater than 6, that adheres directly to the semiconductive plate 10A.Later 10B may be made of an elastomer that is a very good electricalinsulator, in which case the composite plate may be obtained byco-extruding its two layers.

The flexible composite plate 10 is wrapped around the connector 9 andthe stripped end of the insulation of each cable, with itssemiconductive layer 10A pressed against the connector and in intimateelectrical contact therewith. Provision is made for the plate to be oflength equal to or slightly greater than the overall length of the twostripped and interconnected conductors of the cables. Provision is alsomade for it to be of width equal to or greater than the peripherallength of the connector 9 used, and advantageously of any otherconnector that could be used for the two cables or for other cables, soas to be wrapped through at least one full turn around the connectorinterconnecting the cables in question. The dimensions of the compositeplate are defined by those of its layer 10B.

In this embodiment, the splice body 11 is a three-layer tubular elementcomprising a voltage-gradient inner layer 11A, an insulatingintermediate main layer 11B, and a semiconductive outer layer 11C, eachlayer being of uniform thickness, and the three layers being of the samelength and advantageously co-extruded. The voltage-gradient inner layer11A is preferably made of an elastomer having high permittivity.

In a variant, the splice body is two-layer and comprises theabove-mentioned insulating main layer and the above-mentionedsemiconductive outer layer only.

The splice body 11 is radially deformable, and it is preferablymechanically shrink-fittable.

The electrical shielding 12 is also a tubular element which is formed byresilient metal trellis-work. The outer protection 13 is a resilientinsulating elastomer sleeve, and it is preferably mechanicallyshrink-fittable. The electrical shielding and the outer protection areadvantageously pre-assembled in the factory so that they form anassembly with the splice body, which assembly can be directly installedon site on the cables as interconnected and equipped with the plate 10around the connector.

An embodiment of the two-layer plate 10 is shown in FIG. 2, the platebeing shown before it is installed in the splice. The layer ofnon-conductive material 10B is constituted by a mastic plate, and thelayer of semiconductive material 10A is constituted by a plate made ofelastomer that has been rendered semiconductive, the two plates beingmutually superposed and secured to each other directly. The corners ofthe semiconductive plate are cut off so as to be substantially rounded.

As shown in FIG. 2, provision is made for the mastic plate 10B to beslightly wider and longer than the semiconductive plate 10A. Thisfacilitates installation of the composite plate 10 around the connector,by enabling it to be retained initially via one of its longitudinaledges made entirely of mastic, or via its only longitudinal edge madeentirely of mastic, which edge adheres directly to the connector and tothe stripped ends of the insulation of the cables, so that it can thenbe wrapped more easily around the connector and the insulation. Saidedge is deformable and flattened out longitudinally so as to prevent astepped transition from forming on the connector. The other longitudinaledge of the composite plate is also advantageously made entirely ofmastic so as to be flattened out, thereby likewise preventing anotherstepped transition from forming along the outside of the composite plateas installed. The two end edges of the composite plate are alsopreferably defined by those of the mastic plate 10B only, so as to beflattened out over the ends of the insulation of the cables, therebydefining gradual transitions between the stripped insulation of thecables and the composite plate as installed.

The width of the semiconductive plate 10A may be considerably smallerthan that of the mastic plate 10B, while nevertheless remaining largerthan the overall width of one or more longitudinal zones containingdepressions on the periphery of the connector, so as to cover entirelyand extend beyond the zone(s). The semiconductive plate is notnecessarily centered over the width of the mastic plate 10B.

In a variant relative to FIG. 2, the edges of the mastic plate and theedges of the superposed semiconductive plate are in register with oneanother. In which case, one of the longitudinal edges of the compositeplate may be folded inwards, or an adhesive strip may be used so as toenable the edge to be retained on the connector and on the stripped endsof the insulation of the cables, thereby making it easier to wrap thecomposite plate around them.

When the composite plate is formed of two co-extruded layers, anadhesive strip or a bead of glue may be used at the beginning or at theend of installation of the composite plate, for retaining one of thelongitudinal edges on the connector and on the stripped ends of theinsulation of the cables, and for maintaining the plate as installedwrapped therearound.

FIG. 3 shows a strip of adhesive material 14, preferably made ofadhesive ordinary mastic, and serving to fix the above-mentionedcomposite plate along the connector. Preferably, the strip is also usedto fill any deep depressions on the connector used. It is then laidalong such depressions and it is covered by the semiconductive layer ofthe composite plate which is fixed to the strip for the purposes offixing the composite plate, and which is wider and longer than the stripso as to cover the strip entirely, and so as also to be in directcontact with the connector at least all around the strip and around anyunderlying voids that might remain at the depressions.

In the splice shown in FIG. 1, the composite plate 10 is wrapped aroundthe connector through a single full turn with its longitudinal edgesoverlapping. Its outer plate or layer of material that is notelectrically conductive 10B thus finds itself interposed between thesplice body 11 and the inner plate or layer of material that issemiconductive 10A. It makes it possible both to avoid any air bubblesextending between the splice body and the inner plate or layer ofsemiconductive material 10A, and also to reduce the electrical stressesat the ends of the inner plate or layer of semiconductive material 10A.

In addition to being easy and quick to install, the composite plateoffers the advantage of requiring no tool for fitting it, and therebyavoiding any extra cost or risk of damaging the cables, or otherdangers.

Provision is made for the composite plate to be wide enough to fitdirectly over various interconnected cable sections, and over varioustypes of connector, in particular crimpable or boltable types, thatmight be used, by its longitudinal edges overlapping to various extents,or by it being wrapped through a plurality of turns around the connectedused.

The same composite plate also makes it possible for an extruded splicebody to be used that has no semiconductive inner layer which, when it ispresent, is removed along the end portions of the body and remains overits middle portion only. Furthermore, such a composite plate, whoselayer of non-conductive material is constituted by a layer of mastic, isvery well suited to being associated with a mechanically shrink-fittablesplice body, or with the pre-assembled assembly that it forms with theelectrical shielding and the outer protection, which body or assemblycan be installed without using a flame which could soften the mastic andthen cause it to crack subsequently.

Independently of the above advantages, the splice of the invention makesit possible to achieve a very substantial improvement in breakdownstrength. This can be shown by the test results given which express thepartial discharge levels prior to heating cycles in splices of theinvention, and in splices that are comparable except that each of themincludes a semiconductive tube or a high-permittivity mastic around theconnector, instead of the composite plate.

In particular, these partial discharge levels, as expressed inpicocoulombs remain greater than 500 pC at 21 kV when a semiconductivetube is used around a crimped connector, and remain greater than 30 pCat 21 kV and greater than 50 pC at 24 kV when a high-permittivity masticis used around the same connector, but they are less than 5 pC at 21 kVand less than 10 pC at 24 kV when said composite plate is used aroundthe connector. With a bolted connector, the levels remain greater than1,000 pC at 21 kV, when a semiconductive tube is used around theconnector, and they are reduced to less than 10 pC at 24 kV and to lessthan 5 pC at 21 kV when the composite plate is used.

What is claimed is:
 1. A power cable splice comprising:two cables, eachof which comprises a conductor, insulation, a semiconductor screen, ametal screen, and an outer sheath, and has an end portion that has beenstripped in successive steps; a metal connector interconnecting thestripped conductors; a flexible two-layer composite plate whichcomprises a first layer of at least semiconductive material, and asecond layer of a material that is not electrically conductive, andwhich has a length not less than the length of the stripped andinterconnected conductors, and a width not less than a peripheral lengthof said connector, said plate being laid along and wrapped andmaintained around said connector with said first layer being in contactwith the connector; a tubular splice body surrounding said compositeplate around said connector and extending on both sides over thestripped insulation of the cables; and electrical shielding surroundingthe splice body and electrically connected to the metal screens of thecables.
 2. A splice according to claim 1, wherein said composite plateis an extruded composite plate.
 3. A splice according to claim 1,further including a strip made of an adhesive material and associatedwith said composite plate for fixing it along said connector.
 4. Asplice according to claim 3, wherein said strip is laid along externaldepressions in said connector, and it is covered by said first layer ofthe composite plate, said first layer having dimensions that are largerthan those of said strip.
 5. A splice according to claim 1, wherein saidsplice body includes an insulating main layer and a semiconductive outerlayer.
 6. A splice according to claim 5, wherein said splice bodyfurther includes a voltage-gradient continuous inner layer made of amaterial having high permittivity.
 7. A splice according to claim 5,wherein said splice body is a mechanically shrink-fittable element.
 8. Asplice according to claim 7, wherein said splice body and saidelectrical shielding are constituted by a preassembled assembly that ismechanically shrink-fittable.
 9. A power cable splice comprising:twocables, each of which comprises a conductor, insulation, a semiconductorscreen, a metal screen, and an outer sheath, and has an end portion thathas been stripped in successive steps; a metal connector interconnectingthe stripped conductors; means that are electrically conductive at leastin part and that surround said connector; a tubular splice bodysurrounding said means and extending over the ends of the strippedinsulation of the cables; and electrical shielding surrounding thesplice body and electrically connected to the metal screens of thecables, wherein said means are constituted by a flexible two-layercomposite plate which comprises a first layer of at least semiconductivematerial, and a second layer of a material that is not electricallyconductive, and which has a length not less than the length of thestripped and interconnected conductors, and a width not less than aperipheral length of said connector, said plate being laid along andwrapped around said connector with said first layer being in contactwith the connector, and wherein said composite plate is made up of asemiconductive elastomer plate defining said first layer, and of amastic plate defining said second layer, the two plates being mutuallysuperposed and secured to each other.
 10. A splice according to claim 9,wherein said second layer defines the dimensions of said compositeplate, and its length is significantly longer than that of the strippedand interconnected conductors.
 11. A splice according to claim 9,wherein said first layer has at least one of its dimensions smaller thana corresponding dimension of said second layer.
 12. A splice accordingto claim 9, wherein said mastic plate is made of a mastic having highpermittivity, at least about
 6. 13. A splice according to claim 9,further including a strip made of an adhesive material and associatedwith said composite plate for fixing it along said connector.
 14. Asplice according to claim 13, wherein said strip is laid along externaldepressions in said connector, and it is covered by said first layer ofthe composite plate, said first layer having dimensions that are largerthan those of said strip.
 15. A splice according to claim 9, whereinsaid splice body includes an insulating main layer and a semiconductiveouter layer.
 16. A splice according to claim 15, wherein said splicebody further includes a voltage-gradient continuous inner layer made ofa material having high permittivity.
 17. A splice according to claim 15,wherein said splice body is a mechanically shrink-fittable element. 18.A splice according to claim 17, wherein said splice body and saidelectrical shielding are constituted by a preassembled assembly that ismechanically shrink-fittable.